How do you tell when the tubes are broken in?

In another thread another member pointed out that it takes 100 hours for tubes to break in. I have to believe that quantity of hours is not exact but perhaps an average. Plus I imagine most people don't log the hours and keep a running total.

The other day I said I had about 20 hours to go before my Gold Lion KT-88's were broken in. When I installed those I also installed a Gold Lion GZ34 (I think) rectifier to replace the Webber SS rectifier.

Last night while listening after about an hour the music in the room seemed to sound as of the instruments and the singers voice were in the room rather than coming out of the two boxes.
They also sounded more lifelike and coming from different places in the room. I know a lot depends on the recording technique but for the most part as long as it wasn't recorded using the Spector based 'wall of sound' technique instruments had a source in the room.. To me anyway.

What is it that makes you believe the tubes have been conditioned?

There are a few things that may apply to signal tubes, but will not apply to rectifiers in any meaningful way:

a) Contaminants in the materials that 'boil' out of the tube at first use. This could include manufacturing lubricants, residue from packing, handling and other materials. The idea is that these contaminants react with the getter material becoming inert.

b) Residual gases as above.

c) Settling and clearances - metals that are 'worked' in the manufacturing process become hardened, especially at flex points. And as you know many of the fine connections are spot-welded - mixing point-source annealing (softening of metals by heat) with work-hardened bends. The overall heating of the tube over time relieves stresses, which will affect clearances in a small way.

These are the 'biggies' in the aging process.

Rectifiers are special cases as either they work, or they do not work. So their break-in period as it may actually affect the unit they are in is over in a matter of minutes.

In my opinion - and this is over more than 40 years in the hobby - the *actual* break-in period of a well-made tube is less than 10 hours, and if used continuously, probably less than 5 hours. Enough time for the chemical reactions to take place and the stresses to settle. Poorly made tubes are an entirely different matter as with them it will be a close-run thing between 'break-in' and 'failure mode'. Things that come to mind are thin filaments and minimal treatment of same - thorated tungsten comes in many grades but is costly in the first place - as are any of the alternatives. Poor quality spot-welds and internal connections - nothing like built-in obsolescence. And, of course, poor manufacturing care - leaks around the pins and such.

It is perfectly possible to design a vacuum tube that is able to last for tens of thousands of hours and withstand all kinds of abuse. The incremental manufacturing cost is not great - probably less than 30%, if even that. But then consider the issue from 30,000 feet. You are a maker of tubes catering to a tiny percentage of a tiny population. Tooling is expensive. Skills required are specific and difficult. QC is also difficult. Processes are expensive in energy and time - and the equipment requires warm-up and so forth. Meaning that keeping a factory operating profitably requires a significant throughput - and how does one get that throughput? A doughnut factory has no throughput issues - their product is 'done' in 24 hours, if that. Makers of Rolls Royces justify a minimal throughput by high prices and exotic products. But with those tube makers - it is a close run thing between sufficient throughput and cost. Reducing tube life is a simple way to increase throughput *AND* reduce cost. Not price. Cost.

Back when tubes were 'it', pretty much everyone used them - and equipment that required them from televisions to elevator controls were being made in their uncounted millions. So, manufacturers could actually compete on quality. Add the military and QC, materials and more became even more of an art-form. Not so today. NO manufacturer is required to make a "good" tube in the same way as EVERY manufacturer had to do so in... say.... 1950. With exceptions, of course. We are not discussing microwave ovens. X-Ray tubes, Geiger counters or similar, after all.

Ah, well.

Thank you for explaining what actually happens during the break in period. I imagine that the way the tubes are conditioned are also factors for how long the tube may last along with how it sounds as well. Such as how an automobile performs and how long it lasts as well.

However, since another forum member mentioned that brand new unconditioned tubes do not sound good, my question is more along the lines of the sonic changes that a person hears after the tubes conditioning process has completed.

After posting this question I'm thinking that the tubes sonic characteristics change in the course of its lifetime. These changes may be very subtle after conditioning and then change more rapidly as the end of its life approaches.

Please note the interpolations.

Dogstar wrote:Thank you for explaining what actually happens during the break in period. I imagine that the way the tubes are conditioned are also factors for how long the tube may last along with how it sounds as well. Such as how an automobile performs and how long it lasts as well.

However, since another forum member mentioned that brand new unconditioned tubes do not sound good, my question is more along the lines of the sonic changes that a person hears after the tubes conditioning process has completed.

This is a very subjective thing. But even as such, not to be discounted. Most of us here are old enough to remember the standard incandescent lamp - the kind that got really hot and used a tungsten filament. As they aged, they would develop a black coating as well as dim down a little bit. This same phenomenon takes place within a tube, over time. In addition the emitter (Cathode or Filament for a directly heated tube) gradually loses its ability to emit as the plate becomes more and more contaminated with elements from the cathode and filament (the black stuff in a light bulb). Over time, this reaches a point where the tube is no longer useful. *SNARK WARNING*: It is my opinion that a 'new' tube has a very dry sound, AKA Neutral. About the same complaint that many have about solid-state amps. It is also my opinion that this is better described as 'No Sound", meaning that the underlying signal is actually more clearly heard. As the tube ages, it becomes more "tubey" which some describe as "sounding better". This would explain why so many hours are required to reach that state.  

After posting this question I'm thinking that the tubes sonic characteristics change in the course of its lifetime. These changes may be very subtle after conditioning and then change more rapidly as the end of its life approaches.

This progression is non-linear. Or, at least it used to be. Back when tubes were tubes and dinosaurs walked the earth, as tubes aged out the getter flash became less and less, the plate more and more contaminated and the cathode less and less able to emit. But this took a LONG time and could actually be measured by the remaining getter flash. The first 10,000 hours got to about 40% of visible flash, at which point the life of that tube could be measured in multiples of minutes, not hours. Today, I would guess that the getter flash is as minimal as all the other parts in a newly made tubes. Again, makers being few, demand being even fewer and competition being nil, there is no incentive for them to make a Lifetime (with apologies to Radio Shack) tube. Another *SNARK WARNING*: And, the tube audio community is busy training its members into the mindset of tubes being consumables on the same order as tissue paper, gasoline and oranges. While they are consumables - once upon a time they were more-or-less comparable to purchasing an automobile. A definite service life, and according to use more-so than age, but not as ephemeral as they are now.